Crystal‐Phase Controlled Epitaxial Growth of NbNx Superconductors on Wide‐Bandgap AlN Semiconductors. Issue 31 (21st September 2022)

• Record Type: Journal Article
• Authors: Kobayashi, Atsushi; Kihira, Shunya; Takeda, Takahito; Kobayashi, Masaki; Harada, Takayuki; Ueno, Kohei; Fujioka, Hiroshi
• Is Part Of: Advanced materials interfaces. Volume 9:Issue 31(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-21
• Subjects: AlN -- crystal structure -- epitaxial interfaces -- NbN -- semiconductors -- superconductors -- transition metal nitrides; Materials science -- Periodicals; 620.11
• DOI: 10.1002/admi.202201244
• Languages: English
• ISSNs: 2196-7350

Abstract

Abstract: The structural similarity between NbN x and AlN facilitates the integration of superconductors into semiconductor optoelectronic devices. The abrupt interface between wide‐bandgap AlN and superconducting NbN x is essential for future nitride quantum devices, such as Josephson junction‐based quantum bits. In this study, the fundamental properties of NbN x epitaxially grown at various temperatures on atomically flat AlN/sapphire template substrates are investigated. It is found that with increasing epitaxial growth temperature, the nitrogen content of NbN x films grown on AlN decreases, resulting in a change in crystal structure from δ‐ to β‐ via ε‐ and γ ‐type. Microstructural analysis reveals that NbN x thin films epitaxially grown at high temperatures crystallize into a pure hexagonal β‐type and have atomically flat surface and the same in‐plane lattice constant as AlN. The technology for growing high‐purity NbN x films with flat interfaces and surfaces on AlN can contribute to the integration of nitride semiconductors and superconductor hybrid devices. Abstract : The crystal phase of NbN x films on AlN is controlled by epitaxial growth temperature. By sputtering at a very high temperature, phase‐pure β‐type NbN x is epitaxially grown on an AlN surface. The NbN x /AlN interface is abrupt, and β‐NbN x develops from the initial layer. The crystalline interface facilitates the coherent growth of NbN x on AlN.